Future CT scanning technology will involve ultra-fast scanning speeds and fully-three-dimensional scanning configurations. A major requirement for the realization of such advanced scanning concepts is the need for a fast, low-cost, detector array technology with the dynamic range linearity and good efficiency required in the x-ray transmission computed tomography. We believe the best approach will be to replace the tube detectors of most current scanners (phototubes, Xenon chambers, etc.) with solid-state devices that can be fabricated in 2-dimensional arrays. Specifically we will investigate the combination advanced fast scintillation crystals with special PIN-photodiode-preamplifiers. Scintillation-photodiode detectors have already been introduced into two commercial CT systems. However, these detectors are limited by afterglow considerations to relatively long sample times resulting in scan speeds in the 2-5 second range. High speed scanners under development at the Mayo Clinic and at our institution will have scan speeds in the 10-50 millisecond range and require the development of a completely new approach. We propose to work closely with crystal and photodiode vendors to evaluate a variety of detector combinations. After selection of the most promising components, a small prototype detector array will be assembled and tested. The final test will involve acquisition and reconstruction of phantom transmission data using an existing computer data acquisition system. If the tests are successful, a full scale CT two-dimensional detection system will be designed in the third year. Funds to construct and test the full array will be available from other grants and are not requested here.